Wear-resistant power metallurgy nickel-base alloy

ABSTRACT

A wear- and abrasion-resistant article of sintered metal powder consists of chromium from about 23 percent to about 29 percent, tungsten from about 8 percent to about 15 percent, cobalt from about 8 percent to about 15 percent, molybdenum from about 8 percent to about 15 percent, carbon from about 1.65 percent to about 5 percent, boron up to about 1 percent, manganese up to about 1.3 percent, silicon up to about 1.3 percent, iron from about 10 percent to about 17.5 percent, and the balance nickel in amount at least about 20 percent and incidental impurities.

ite States Foley et alil atent 1 WEAR-RESISTANT POWER METALLURGY NICKEL-BASE ALLOY [75] Inventors: Edward M. Foley; Robert F. Polk,

both of Kokomo, Ind.

[52] US. Cl 29/182, 29/1825, 75/171, 75/134.5 [51] Int. Cl. C220 l/04, C220 19/00 [58] Field of Search 29/182, 182.5; 75/171, 75/134 F [56] References Cited UNITED STATES PATENTS 3,068,096 12/1962 Elbaum 75/171 3,562,024 2/1971 Smith 3,644,153 2/1972 Rausch et a1 75/134 F OTHER PUBLICATIONS Jones, W. D., Fundamental Principals of Powder Met- [4 1 Oct. 1, 1974 allu gy, London, Edward Arnold, 1960, p. 2l2213, Tn 695 J.6.

Primary Examiner-Carl D. Quarforth Assistant ExaminerR. E. Schafer Attorney, Agent, or FirmBuell, Blenko and Ziesenheim 5 7] ABSTRACT A wearand abrasion-resistant article of sintered metal powder consists of chromium from about 23 percent to about 29 percent, tungsten from about 8 percent to about 15 percent, cobalt from about 8 percent to about 15 percent, molybdenum from about 8 percent to about 15 percent, carbon from about 1.65 percent to about 5 percent, boron up to about 1 percent, manganese up to about 1.3 percent, silicon up to about 1.3 percent, iron from about 10 percent to about 17.5 percent, and the balance nickel in amount at least about 20 percent and incidental impurities.

8 Claims, 2 Drawing Figures PATENIEDUCT 1 1574 Carbon Fig.2.

o zmsxoom 39 B: QEm Eoom Carbon WEAR-RESISTANT POWER METALLURGY NICKEL-BASE ALLOY This invention relates to articles of wear and abrasion-resistant alloys. It is more particularly concerned with such articles sintered from powder of a nickelbase alloy.

Numbers of abrasion and wear-resistant alloys have been developed for articles subject to those service conditions. They exhibit high tensile strength and great hardness at temperatures as high as I,200F. to l,400F., impact strength of the order of 3 to 5 foot pounds, and in general are difficult or impossible to work. Consequently, they have been used in the form of castings which are sometimes ground to dimensions, or hard-surfaced deposits produced by welding.

The greater number of those alloys are cobalt-base alloys containing substantial amounts of chromium, tungsten and sometimes molybdenum. Cobalt is an expensive constituent and attempts have been made to substitute therefor, at least in part, other less expensive elements. A nickel-base alloy which for many purposes is used in place of the cobalt-base alloys is disclosed in U.S. Pat. No. 3,068,096, issued to J. K. Elbaum et al., on Dec, 1 l, 1962. Its hardness, however, drops off somewhat below that of the best of the cobalt-base alloys at temperatures above about 1,200F. This would seem to be because of a deficiency of hard carbide constituents. Although several cobalt-base alloys contain carbon in amounts on the order of 2.5 percent, the carbon content of the alloy of Elbaum et al., must be held below about 1.6 percent, according to the patentees. Compositions with more carbon are said to be undesirable and to have reduced impact resistance. The patentees attribute this behavior to the M C type of carbides which they say are formed when the carbon content exceeds the critical value.

While casting and hard-surfacing techniques are satisfactory for the production of wear-resistant articles of large and moderate sizes, they are not well suited for the production of a multiplicity of relatively small articles. Consequently, attempts have been made to apply the techniques of powder metallurgy to the production of articles abrasionabrasion and wear-resistant alloys, including those of the Elbaum et al., patent. One of those techniques comprehends forming an article of the desired shape by consolidating a powder of the desired alloy and then sintering the green compact to produce a solid article having a density comparable to that of a cast article. The alloy powder is loaded into a die of the desired shape and is there consolidated under pressure to a green compact that will withstand the shrinkage stresses and other stresses incidental to sintering. The green compacts are then sintered in a non-oxidizing atmosphere and in this way a large number of duplicate articles can be economically produced.

A number of the cobalt-base and other types of wearresistant alloys can be fabricated by the powder metallurgy technique summarized above. The nickel-base alloy of the Elbaum et al., patent, however, is very difficult to fabricate into articles in this way. To achieve a density of 95% or better of cast density, which is a requirement for most articles of the type in question produced by powder metallurgy techniques, and a Rockwell C hardness of 40 or better, the compacts must be sintered at a temperature of 2,300F. or more, plus or minus a few degrees. The width of the sintering range is influenced by the size of the powder particles and may be as narrow as plus or minus 10F, which renders the process scarcely more than a laboratory operation. Grinding of the particles to a smaller size, which is a tedious and expensive operation, widens the sintering range to plus or minus 20 or 25F. This is still quite narrow for commercial practice and requires rather elaborate furnace controls.

In the commercial production of a multiplicity of articles by powder metallurgy processes it is desirable that the sintering operation be carried out as a continuous operation. This is economically accomplished by loading the green compacts into metal trays and passing the trays one after another through a tunnel furnace in which the desired atmosphere is maintained and in which the articles remain at temperature for the time required for sintering to be completed. A convenient way to effect this operation is to use the tray of green compacts being introduced into one end of the furnace to push out a tray of sintered compacts from the other end of the furnace. The furnace length, of course, may be a multiple of the tray length. As it happens, however, the metal trays normally used for this purpose, when heated to temperatures of 2,300F. or thereabout, tend to buckle and deform when used to push another tray through the furnace. They have adequate strength at temperatures F. or so lower. It is, therefore, advantageous from the production standpoint to sinter the compacts at temperatures which are safe for the trays. From this standpoint, the actual value of the safe temperature is not too important.

It is an object of our invention to provide wearresistant articles sintered from a nickel-base allow pow der. It is another object to provide sintered articles having a composition similar to that of the Elbaum et al., patent. It is another object to provide such articles of a greater hardness than has heretofore been available. It is still another object to provide sintered articles of a composition which sinters to satisfactory density over a broader temperature range than has been the case. It is a further object to provide such articles which sinter at lower temperatures than have before been employed. Other objects of our invention will appear in the course of the description thereof which follows.

We have found that articles sintered from an alloy powder of the composition of the Elbaum et al., patent but with higher carbon content and preferably a relatively small boron content do not have the brittleness mentioned by Elbaum et al., have a higher hardness than their articles, and sinter at a lower temperature, over a temperature range, depending on their carbon content, which is many times as broad as that of prior art compositions.

The composition of the articles of our invention is set out in the accompanying Table 1.

TABLE 1 ALLOYS OF THIS INVENTION (IN WEIGHT PERCENT) ALLOYS OF THIS INVENTION The alloy powder which we employ is preferably produced by the atomization of a melt of the desired composition. This melt is heated to a temperature of 200F. or so above its fusion temperature in a crucible. Preferably, this melting is carried out in vacuum or under a blanket of inert gas such as argon. The melt is then poured into a preheated refractory tundish which is fashioned with a small-diameter nozzle in the bottom through which the stream of metal flows into an atomizing chamber. The stream emerging from the nozzle is broken up into fine particles by a high-pressure jet of inert gas, or of water, which makes contact with the molten stream just below the nozzle. The particles or droplets are almost instantaneously quenched by the atomizing fluid and fall into a reservoir in the bottom of the atomizing chamber. Only the fraction is used which passes through a 30 mesh screen. These particles are approximately spherical in shape and about 25 percent to 35 percent of the particles are -325 mesh. When articles of high density are to be produced we use only the -325 mesh fraction.

We then blend or mix the powder with a solid binder and a solvent. We prefer to use polyvinyl alcohol as a binder for our powder, but other solid binders which are known to the art are employed. Examples are camphor, methyl alcohol, paradichlorobenzene, chloroacetic acid, napthalene, benzoic acid, phthalic anhydride, glycerine, Acrowax C which is a proprietary compound, the ethylene oxide polymers sold as Carbowax, synthetic gums such as acrylamide, and metal stearates. The solvent for the binder must be appropriately chosen. Water is satisfactory for water-soluble binders.

The blending of the powder and binder particles is accomplished in any suitable mixing apparatus. The amount of binder is not critical, and a few percent by weight is sufficient. The plastic or putty-like blend of particles, binder and solvent is then consolidated into agglomerates, preferably by extrusion, but other methods, such as roll briquetting, may be employed.

The extrusions are dried, crushed in a roller crusher, hammer mill or the like, and screened. The 100 mesh fraction of crushed extruded bindered powder is largely fines. From about 60 percent to 80 percent of the particles are 325 mesh with corresponding apparent densities of about 2.0 to 3.3 grams per cc. Both the percentage of fines and the apparent density of this material are, however, less than those of the milled powder.

The agglomerates of powder and binder are pressed in dies or molds of the desired shape under a pressure of about 50 tons per sq. inch. The compacting pressure can be as low as tons per sq. inch or as high as 70 tons per sq. inch, the density of the green compacts being higher at higher compaction pressures. At a compaction pressure of 20 tons per sq. inch, compact density is about 56 to 58 percent of cast density, and at tons per sq. inch it is 70 to 72 percent of cast density.

A finished article of the desired density is obtained by sintering the compact in vacuum or reducing atmosphere at a temperature between the solidus and liquidus temperatures of the alloy. Sintering can be completed in about an hour but if the time is extended to two or at most three hours the temperature can be reduced somewhat without impairing the properties of the article. Compacts properly sintered have densities of 98 percent or better of cast density,

Our process also contemplates grinding, when necessary, of part or all of the powder particles resulting from the atomization of a melt as above described, so as to convert a larger fraction of the powder to 325 mesh.

Nine experimental alloys were prepared from a single master alloy in the manner described herein. All of the alloys contained essentially:

about 26% Chromium about 10% Tungsten less than 1.0% Silicon less than 1.0% Manganese about 0.5% Boron about 10% Cobalt about 10% Molybdenum about 12.5% lron Balance Nickel and impurities TABLE 2 EXPERIMENTAL ALLOYS Carbon Content Hardness Sintering Range Alloy No. Rc F It will be observed that the alloys A and B, which have the compositions of the alloys of Elbaum eta1., except for the boron addition, sinter at appreciably lower temperatures than those previously mentioned for the same alloys without boron. The permissible range of sintering temperatures, however, is the same for the boron-containing alloys as for those without boron for the same particle size of the powder. In our alloys, which also sinter at the lower temperatures above mentioned, the permissible range of sintering temperatures widens very substantially as the carbon content of the alloy is increased above about 1.65 percent, and the lower margin of the range falls off as the carbon content is increased above this value. The upper margin of the range increases until the carbon content reaches about 2.4 percent after which it also falls off. This is shown graphically in FIG. 1, which for comparison purposes is extended into the carbon range of the Elbaum et al., patent. While the alloy of Elbaum et. al., with their preferred carbon content of 1.4 percent can be sintered when produced by the powder metallurgical techniques here described only between 2,210F. and 2,230F. a mere range our alloy here described, with a carbon content of 2.4 percent, for example, can be sintered at temperatures between 2,190F. and 2,270F. Our alloy with a carbon content of 4.2 percent can be sintered at temperatures as low as 2,110F. and as high as 2,210F.

We have also found, unexpectedly, that in articles of the composition here disclosed produced from metal powder in the way here described the undesirable M C type carbides mentioned by Elbaum et al., do not seem to form in significant amounts until the carbon content of the alloy exceeds about 5 percent. It may be that this benefit results from the improved homogeneity which our articles exhibit, as compared with cast articles, but we do not commit ourselves to this explanation. The articles of our invention have both room temperature and elevated temperature hardness higher than the alloys of the Elbaum et al., patent and impact strengths of the same order as their alloys.

FIG. 2 shows graphically how the Rockwell C scale room temperature hardness of our alloy increases with an increase in its carbon content. For comparison purposes, this curve also is extended into the composition range of the Elbaum et al., patent. The hardness is seen to increase almost linearly until the carbon content of the alloy reaches about 3.3 percent, beyond which the graph begins to bend over and reaches its peak at about 4 percent carbon content. The room temperature hardness of our alloy with this carbon content is about 57 Rockwell C scale. The maximum carbon content of our alloy is effectively limited by another consideration. As we have mentioned, we prefer to use alloy powder produced by atomizing a melt of the desired composition. When the carbon content of such a melt of our alloy is increased beyond about 5 percent the melt loses fluidity and becomes viscous so that atomization is impossible.

The boron content of our alloys is not critical. As we have pointed out, boron additions do not increase the allowable range of sintering temperatures of the alloys here concerned, but do lower the absolute value of those temperatures. The higher carbon contents of our alloys, on the other hand, bring about both broadening of the range of sintering temperatures and a lowering of the minimum sintering temperature. Thus, as the carbon content of our alloys is increased, their boron contents becomes less significant. We prefer to include boron in amounts of about 0.5 percent in our alloys, but as little as about 0.05 percent is effective, and there seems to be no advantage in using boron contents above about 1 percent. Our alloys may be made with no boron addition if the apparatus used for sintering can withstand the necessary sintering temperatures.

The nickel content of our alloy should be at least 20 percent by weight and the amounts of the other elements listed should be adjusted accordingly within the ranges specified for each element. Contrary to the teaching of the Elbaum et al., patent, cobalt cannot be replaced by any other element but must be present within the ranges indicated. The elements other than carbon which are specified by Elbaum et al., act in the same way as they have described. The modifying elements mentioned in Table 1 consist of zirconium, lanthanum, yttrium, vanadium, beryllium, magnesium and rare-earth metals. The presence of one or more of these elements in the amounts tabulated improves the working characteristics such as ductility and oxidation resistance of the alloy. The optional elements mentioned in that Table consist of tantalum, columbium, titanium, aluminum, hafnium, and copper. The presence of these elements in the amounts tabulated is not detrimental to the hardness, impact resistance or sinterability of the alloy.

The alloys from which the data of FIGS. 1 and 2 were derived had approximately nominal compositions as set out in the Table, except for carbon content, and contained no modifying or optional elements.

Generally speaking, for all the alloys here mentioned the curve of room temperature hardness against sintering temperature and the curve of article density against sintering temperature peak together, at a temperature below the liquidus temperature of the alloy, and the sintering temperature limits are chosen to bracket those peaks reasonably symmetrically. The upper limit must, of course, be below the temperature at which the green compact begins to slump or lose its shape, and the lower limit is set at a temperature which produces an article density of at least of cast density in the desired sintering time.

In the foregoing specification we have described a presently preferred embodiment of this invention, however, it will be understood that this invention can be otherwise embodied within the scope of the following claims.

We claim:

1. An article of sintered metal powder consisting of chromium from about 23 percent to about 29 percent, tungsten from about 8 percent to about 15 percent, cobalt from about 8 percent to about 15 percent, molybdenum from about 8% to about 15 percent, carbon from about 1.65 percent to about 5 percent, boron up to about 1 percent, manganese up to about 1.3 percent, silicon up to about 1.3 percent, iron from about 10 percent to about 17.5 percent, and the balance nickel in amount at least about 20 percent and incidental impurities.

2. The article of claim 1 including boron from about 0.05 percent to about 1 percent.

3. The article of claim 1 containing chromium from about 25 percent to 27 percent, tungsten from about 9 percent to 11 percent, carbon from about 1.65 percent to about 4.2 percent, silicon up to about 1 percent, manganese up to about 1 percent, boron up to about 1 percent, cobalt from about 9 percent to about 11 percent, molybdenum from about 9 percent to about 11 percent and iron from about 11.5 percent to about 13.5 percent.

4. The article of claim 3 including boron from about 0.05 percent to about 1 percent.

5. The article of claim 1 containing chromium about 26 percent, tungsten about 10 percent, carbon about 1.65 percent to 4.2 percent, silicon about 1 percent, manganese about 0.75 percent, boron about 0.5 percent, cobalt about 10%, molybdenum about 10% and iron about 12.5%.

6. The article of claim 1 including one or more of the elements zirconium, lanthanum, yttrium, vanadium,

beryllium, magnesium, and rare-earth metals, in amounts aggregating not more than about 1 percent.

and copper, in amounts aggregating not more than about 10 percent.

8. The article of claim 1 in which the metal powder is that resulting from the atomization of a melt of the 7. The article of claim 1 including one or more of the 5 composition claimed. 

1. AN ARTICLE OF SINTERED METAL POWDER CONSISTING OF CHROMIUM FROM ABOUT 23 PERCENT, TO ABOUT 29 PERCENT, TUNGSTEN FROM ABOUT 8 PERCENT TO ABOUT 15 PERCENT, COBALT FROM ABOUT 8 PERCENT TO ABOUT 15 PERCENT, MOLYBDENUM FROM ABOUT 8% TO ABOUT 15 PERCENT, CARBON FROM ABOUT 1.65 PERCENT TO ABOUT 5 PERCENT, BORON UP TO ABOUT 1 PERCENT, MANGANASE UP TO ABOUT 1.3 PERCENT, SILICON UP TO ABOUT 1.3 PERCENT, IRON FROM ABOUT 10 PERCENT TO ABOUT 17.5 PERCENT, AND THE BALANCE NICKEL IN AMOUNT AT LEAST ABOUT 20 PERCENT AND INCIDENTAL IMPURITIES.
 2. The article of claim 1 including boron from about 0.05 percent to about 1 percent.
 3. The article of claim 1 containing chromium from about 25 percent to 27 percent, tungsten from about 9 percent to 11 percent, carbon from about 1.65 percent to about 4.2 percent, silicon up to about 1 percent, manganese up to about 1 percent, boron up to about 1 percent, cobalt from about 9 percent to about 11 percent, molybdenum from about 9 percent to about 11 percent and iron from about 11.5 percent to about 13.5 percent.
 4. The article of claim 3 including boron from about 0.05 percent to about 1 percent.
 5. The article of claim 1 containing chromium about 26 percent, tungsten about 10 percent, carbon about 1.65 percent to 4.2 percent, silicon about 1 percent, manganese about 0.75 percent, boron about 0.5 percent, cobalt about 10%, molybdenum about 10% and iron about 12.5%.
 6. The article of claim 1 including one or more of the elements zirconium, lanthanum, yttrium, vanadium, beryllium, magnesium, and rare-earth metals, in amounts aggregating not more than about 1 percent.
 7. The article of claim 1 including one or more of the elements tantalum, columbium, aluminum, hafnium and copper, in amounts aggregating not more than about 10 percent.
 8. The article of claim 1 in which the metal powder is that resulting from the atomization of a melt of the composition claimed. 